Typically, an LPI (LPG Injection) engine uses liquefied petroleum gas (LPG) as a fuel. The LPG is stored in a fuel tank in a liquid state and is pressurized by a fuel pump disposed in the fuel tank for injection into combustion chambers of an engine. An amount of fuel injected into the combustion chamber is determined based on various vehicle conditions.
If LPG is heated by the heat of an engine, its saturated vapor pressure increases rapidly, such that pressure in a fuel supply line also increases. In particular, after a vehicle has been driven for a long time, fuel exists in the fuel supply line and the engine has a lot of heat, therefore, the fuel pressure in the fuel supply line can rise very high. Such an increase in fuel pressure in the fuel supply line may cause the fuel to leak from a fuel injector. Furthermore, with aging of the fuel injector, leakage of fuel in the fuel injector can substantially increase.
The air/fuel mixture may become substantially rich because of the leaked fuel in a combustion chamber. When an amount of leaked fuel is small the air/fuel mixture is in a combustion range, but when the amount of leaked fuel is substantially large the air/fuel mixture goes beyond the combustion range, and start time is increased because of misfire. Furthermore, the leaked fuel may increase an amount of exhaust emissions, in particular, hydrocarbons.
In LPG engines, conventional fuel control does not consider the leaked fuel, so engine startability and emission characteristics are poor.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.